This invention is concerned with a method for the removal of acid and acid precursor gases and vapors from the gases, by passing the polluted gas through a bed of activated carbon impregnated with caustic.
The acid and acid precursor gases and vapors, the removal of which is accomplished by the novel method of this invention are: halogens, such as bromine, iodine and fluorine, especially chlorine; the corresponding hydrogen halide, especially hydrogen chloride; sulfur oxides (SOx), especially sulfur dioxide and trioxide; nitrogen oxides (NOx), especially nitrogen di- and trioxide; low molecular weight organic acid vapors, such as formic and acetic acids; and esters of organic acids, such as ethyl and amyl acetate.
An impregnated activated carbon suitable for use in the novel method of this invention is an activated carbon impregnated with about 0.5 to about 20% by weight of sodium hydroxide and from about 4 to about 50% by weight of moisture, both based on weight of dry activated carbon. Carbons of this type are fully described in U.S. Pat. No. 4,072,479, the disclosure of which is incorporated herein by reference.
The novel method of this invention has several applications such as providing non-corrosive make-up air for electronic equipment in control rooms, particularly in water treatment plants where the air may have up to a few parts per million of chlorine, and in industrial chemical plants which can provide a great variety of contaminant gases and vapor with corrosive, acidic properties. Another application is treatment of flue gases for removal of acidic components therefrom.
Traditionally, such gas purification needs have been supplied by various methods, such as scrubbing, adsorption or absorption. Now with the present invention there is provided a novel method combining all of the advantages associated with adsorption with enhanced capacities over conventional adsorbents combined with some of the advantages of a scrubbing system.